1. Field of the Invention
The present invention relates to a novel process for the preparation of .gamma.-pyrone derivatives including pyrocomenic acid, [3-hydroxy4(1H)-pyran-4-one and rubiginol, [3,5-dihydroxy-4(1H)-pyran-4-one, which are starting materials for synthesis of maltols useful as food spices as well as additives for cosmetics.
2. Prior Art
Maltols are known to be conventionally produced for example by the following methods:
U.S. Pat. No. 3,130,204 (1947) and Spielman M.A. et al, "J. Am. Chem. Soc.", 1947, 69 2908 disclose the method wherein after hydroxyl groups of kojic acid obtained by fermentation are protected, its primary alcohol group is oxidized, next the protecting group is removed, then the resulting material is subjected to decarboxylation reaction to form pyrocomenic acid, further hydroxymethylated and thereafter reduced to obtain maltols.
Japanese Patent Publication Sho 45-16204 discloses the method wherein 2,5-diketogluconic acid is heated under an acidic condition, the resulted comenic acid is decarboxylated to form pyrocomenic acid, which is followed by the same manners as above to obtain maltols. Shono et al, "Tetrahedron Lett., 1976, 1963 discloses the method wherein furfurals are led to 2,5-dimethoxyfuran derivatives through electlytic reaction, said derivatives are placed under an acidic condition to take place ring-formation reactions, thereby obtaining .beta.-pyrone derivatives, further the resultants are subjected to alkylation, expoxydation and acidic condition to obtain maltols.
As seen above, maltols are produced through a considerably large number of the preparation steps. In addition, their yields are not necessarily satisfactory. Further there are also cases wherein relatively expensive chemicals are used.
In the light of such a present status, the present inventors have extended our studies to develop various methods for economically and simply preparing pyrocomenic acid which is to be the key compound for the preparation of maltols.